My Mac Mini G4 refuses to boot from basically anything. I have a copy of Leopard, as a bootable drive on my thumb drive. I can boot from any computer fine, but the Mac Mini will not boot from it. So, I used Target Disk Mode to install the OS onto the Mini G4, and it installed fine. Disk Utility erased, formatted, ran the install, and the Macbook Pro I had the G4 hooked up to via TDM booted fine off of the Mini's HD. I turned off both, and tried to boot up just on the Mac Mini, and it gave me the ?. I booted using ALT to see any options to boot from, and the screen was empty. I booted from a Tiger installation DVD to try to change my startup disk that way, and the startup disk option DID recognize Leopard on the hard drive. It confirmed to restart using Leopard on the HD, and when it restarted - still the ? What would be the next step to troubleshoot?